GOES-16 GLM data was utilized to help monitor storm activity near the site of the El Paso County Fair during the week of July 14 – July 21. The fair takes place in Calhan, which is in northeast El Paso County. During the late afternoon of July 17, a cluster of thunderstorms approached the fair grounds from the west. Given the potential for rain, breezy winds, and lightning (confirmed in GLM with CG’s confirmed by NLDN), EL Paso County Sheriff’s office was notified at around 2345 UTC. Figure 1 shows a 1-hour long loop updating every 1-minute, while Figure 2 is the same animation but with the break points discussed in the rest of this post.
By 0000 UTC (the middle of the loop), 0.5 degree radar reflectivity showed the eastern edge of a cell moving into Calhan, with NLDN confirming cloud to ground lightning strikes. However, GLM FED indicated lightning activity still well to the west of town. This discrepancy is due to parallax effect inherent in the GLM data. The GLM gridded data in AWIPS is formatted to the 2 km ABI fixed grid, so is influenced by the same parallax effect. In Colorado from GOES-East, lightning objects will appear slightly to the north and west of where it actually is occurring over the surface. Users will need to get used to the degree of the effect in their CWA, and use radar, NLDN, etc to confirm where that lightning is actually occurring.
By 0029 UTC (the end of the loop), radar and NLDN data would indicate Calhan in a gap of thunderstorm activity. However, GLM shows mainly long flashes continuing to extend over and around Calhan, implying a continued lightning threat away from the updraft cores and over the fair grounds.
The Total Optical Energy Product was not found to provide any additional value over FED and AFA in this case.
Bill Line, NWS